Most digital audio and/or video broadcasting systems, particularly those of digital nature like digital terrestrial television and digital satellite television, have the capability of broadcasting audio and/or video contents while restricting the access to selected contents on a user-specific basis; to this purpose, so-called “Conditional Access” (CA) systems are exploited, that allow managing the users' access rights to the broadcast contents. Typically, CA systems are exploited to enable fruition of particular contents, like movies or sport matches or like events, in respect of those users who have properly subscribed and paid for them.
Conditionally enabling a user to access specific broadcast contents typically means that the contents (e.g., a video and/or audio stream) are properly encoded, and that, together with the encoded contents, decoding information necessary for the decoding thereof are broadcast. A detailed description of the use of CA systems in Digital Video Broadcasting (DVB) systems is provided in the European Telecommunications Standards Institute (ETSI) Technical Report (ETR) 289 entitled “Digital Video Broadcasting (DVB); Support for use of scrambling and Conditional Access (CA) within digital broadcasting systems”.
In order to enjoy the broadcast contents, the user needs a receiver, which can be a separate equipment (usually called “Set Top Box” or, shortly, STB) associated with the TV set located at the generic user's premises, or it can be embedded thereinto.
The receiver receives the encoded contents and the associated decoding information, and is adapted to exploit the latter for decoding the contents so as to make it enjoyable by the user.
Usually, CA systems rely on the provisioning to the subscriber users of a personal smart card, i.e. a typically credit-card size support embedding an integrated-circuit chip with data storage and processing capabilities; in particular, the smart card stores data (e.g., passwords, decryption keys, contents fruition enabling data specifying the contents whose fruition is authorized) to be exploited for enabling the decoding of the broadcast contents. The user inserts the personal smart card into a suitable smart card reader of which the STB needs to be provided; the data stored on the smart card and the decoding information broadcast with the encoded contents are exploited for decoding the contents while they are received. If the correct smart card is not inserted in the STB's reader (or if the smart card is not enabled—for example, the smart card has not been activated, or has been deactivated by the contents broadcaster), the fruition of the broadcast contents is denied, and the STB can not decode the received, encoded video and/or audio broadcast streams. This operation is for example described in the document by M. Kuhn entitled “The New European Digital Video Broadcast (DVB) Standard”, published (at the date of filing of the present application) on the Internet at the address www.cl.cam.ac.uk/˜mgk25/dvb.txt. The structure, in terms of functional blocks, of a conventional STB is for example described in the document published (at the filing date of the present application) on the Internet at the address www.drakesvision.com/digi4.htm. Schematizing, the STB includes a front-end functional module that receives the signal from the antenna and retrieves the broadcast data (video and/or audio) streams; a decoder functional module, which, in case the received data stream is encoded, decodes it; a back-end functional module, adapting the decoded signal to the format supported by the TV set. The decoder module interacts with a CA system functional module, requesting thereto the authorization and other information necessary for decoding the received streams. The CA system module interacts in turn with the smart card (inserted in the smart card reader of the STB), on which the user's subscription data and the information necessary for the decoding process are stored.
While receiving an encoded data stream, the decoder module periodically requests to the CA system module the authorization to decode and the information necessary for decoding the encoded stream; the CA system module, in turn, requests the above data to the smart card, and provides them to the decoder module; the decoder module then decodes the encoded stream. These actions are performed, for example repeatedly, during the reception of the video and/or audio contents.
A drawback in the process described above resides in the fact that the enablement to the fruition of the encoded video and/or audio contents is entirely performed in the user's receiver, e.g. in the STB, relying on the data stored on the smart card which is assumed to having been provisioned to the subscriber user. In case a fraudulent user succeeds in tampering its own smart card, so to alter the data stored therein, for example to the extent that the contents' fruition is always considered authorized (e.g., irrespective of which content is being received), or in case the data stored on the smart card are extracted therefrom, making available the information necessary for performing the decoding, or even in case the smart card itself is cloned, the encoded broadcast contents would become fully available to the user, without authorization of the content provider, which not only is not in a position to prevent such an unauthorized, fraudulent exploitation of the contents, but it is not even aware of it.
In WO 01/80460 a method for controlling reception of a digital TV transmission is disclosed, in which the decoding key entitling to the decoding of the digital transmission is transmitted to a subscriber user's wireless terminal device, e.g. a mobile station; the decoding key is then transferred to the receiving equipment (set-top box) and the digital transmission received is decoded with the aforementioned decoding key. The use of the wireless terminal device compensates the smart card required for the decoding of the digital transmission.
In WO 02/096109 a broadcasting receiving equipment is also disclosed, including a control section able to generate return data by including return information data among input data and broadcasting data. The broadcasting receiving equipment further includes a mobile communication section for transforming the return data into mobile communication signals in order to transmit the return data to receivers through a mobile communication network. Return data may include a MAC address given to the broadcasting receiving device; an identifying number given to subscribers or the combination thereof, as an identifier; particulars about trouble detected by the control section.